A liquid crystal display device is one example of display devices that are used as high-definition color monitors for computers and other information devices, and as television receivers. A liquid crystal display device fundamentally includes a display portion in which liquid crystals are sandwiched between two substrates at least one of which is made of transparent glass or the like. In addition, a liquid crystal display device includes a driver for selectively applying voltages to pixel electrodes formed on the substrate of the display portion. Pixels of the respective pixel electrodes are controlled based on the voltage application by the driver.
The display portion generally includes a plurality of gate signal lines, a plurality of source signal lines, and a plurality of pixel electrodes. The gate signal lines, for example, respectively extend in a horizontal direction (main scanning direction), and are aligned in a vertical direction (sub scanning direction). The source signal lines, for example, respectively extend in the vertical direction (sub scanning direction), and are aligned in the horizontal direction (main scanning direction). A plurality of thin film transistors (TFTs) and a plurality of the pixel electrodes are disposed in a matrix at intersection points of the gate signal lines and the source signal lines.
A gate driver outputs voltages (gate signals) to the gate signal lines for turning the TFTs on and off. A source driver outputs voltages (source signals) based on an input image signal to the pixel electrodes via the source signal lines to thereby control transmittance of liquid crystals provided corresponding to the pixel electrodes to values according to the source signals.
A display device smoothly displays images on a display portion by successively switching frame images to be displayed on the display portion, for example, based on image signals input from outside. Conventionally, there is a known display device that determines whether an image to be displayed on a display portion is a still picture or a moving picture, and switches between interlaced scanning and progressive scanning of gate signal lines based on a result of the determination. A display device disclosed in a prior art prevents deterioration of image qualities by progressively scanning gate signal lines when an image to be displayed on a display portion is a moving picture, and attempts to reduce power consumption by interlaced scanning of the gate signal lines when the image is a still picture (See Japanese Unexamined Patent Application Publication No. 2006-064964).
Unfortunately, with the device disclosed in the prior art, when the method of scanning the gate signal lines is switched between interlaced scanning and progressive scanning too quickly, a power-supply voltage changes due to load changes and an influence of a leakage of voltages held in pixels, and thus brightness changes. Therefore, it becomes difficult to smoothly switch images to be displayed on the display portion, which may possibly result in excessive deterioration in image qualities.